Before you said, I have had a good thought of all of those reasons.
I think the first reason you said "they want to offload a big position" is not likely as they are selling for a long time. It is now exceeded more than 10m shares easily changed the hands. There is no substantial holder announcement as well. Some other things also tells me the seller and buyer are the same guys in those bad days. This market is corrupted they can easily do it through different accounts.
As you may remember when the price hit 20.5c, there were no sellers. The buyers were close to 4m and sellers were about 280k. Those guys were panicked and asked ASX to ask NSE to make an anns. And NSE made it, said nothing is new. Then they brought down the price. This is all organized job IMO. There is something very big behind this, I believe.
The second reason; "building their short position until NSE are forced to raise capital down the track at lower levels - which they can then participate in and close their short position" is also not possible IMO. NSE does not need to raise capital at least another year. And they have more than 3 well drilling during this time. The sp can go up to sky at that time.
Anyway, the only thing they tell us "to buy more and more". That my translation from their trading language.
NSE Price at posting:
16.5¢ Sentiment: Buy Disclosure: Held